The present invention relates generally to a technique for controlling the temperature of liquids contained in a vessel for use in a chemical analyzer wherein sample liquids such as blood are photometered colorimetrically, and particularly to a flowcell type vessel with a temperature control device.
For example, in the case of using a flowcell for colorimetric photometry, sample solutions contained in reaction vessels are supplied successively to the flowcell, and a given photometry is performed for the sample solution contained in the flowcell. In this case, in order to test successive samples, sample solutions whose amount is at least sufficient to fill the flowcell are supplied successively to the flowcell while being separated by air from each other. When a sample solution is supplied to the flowcell, the solution is maintained at a predetermined temperature for a given time period by abruptly heating or cooling the solution. Recently, chemical analyzer with high processing efficiency have been made which can treat a very large number of the sample solutions within a short time period. Therefore, in the flowcell, the sample solution must be heated or cooled to the predetermined temperature within a short time period. In addition, the recent chemical analyzers are so contructed as to minimize the sample amount and reagent amount to be used therein as mcuh as possible, and thus the flowcells have been made smaller correspondingly smaller. Therefore, it also is necessary to make the temperature control apparatus in the flowcell and the chemical analyzer small.
Heretofore, proposed method for controlling the temperature of the sample solution in the flowcell has been to use a thermostat, i.e., providing an isothermal liquid tank for the flowcell having a heating and cooling means. In the case of using the isothermal liquid tank, the reaction vessel is placed in a thermo-medium such as water or ethylene glycol, and the sample solution is maintained at a predetermined temperature by controlling the temperature of the thermo-medium. However, in this case, the capacity of the thermo-medium must be several hundred to thousands of times as large as that of the flowcell, and thus the whole system is extremely large in size. It is also necessary to use a large control apparatus to control the temperature of a thermo-medium having such a large capacity, and thus the system becomes expensive. Moreover, when changing or presetting a predetermined temperature, an extremely long time is required until the temperature of thermo-medium reaches the desired temperature, because the thermal capacity of the isothermal liquid tank is extremely large. This means that it takes a very long time for the thermal-medium to reach an equilibrium state when a temperature variation occurs, and that the response characteristics and thus the controlling accuracy of the apparatus become worse.
In order to eliminate the drawbacks mentioned above, there has been proposed in German Patent specification No. 2651356 a vessel shown in FIGS. 1A and 1B. In FIGS. 1A and 1B, a pair of thermo-modules 2a, 2b made of, for example, a Peltier element are arranged on upper and lower surfaces (FIG. 1A) or opposed side surfaces (FIG. 1B) of a flowcell 1 and a pair of temperature sensors 3a, 3b are arranged on side surfaces (FIG. 1A) or upper and lower surfaces (FIG. 1B). A sample solution is supplied to the flowcell 1 through a supplying tube 4, and the sample solution contained in the flowcell 1 is maintained at a predetermined temperature by heating or cooling the thermo-modules 2a, 2b in accordance the output signals from the temperature sensors 3a, 3b. A light flux emitted from a light source 5 is made incident upon a light receiving element 7 through a collimator lens 6 and the flowcell 1 so as to effect a colorimetric photometry, and, after the photometry, the sample solution is discharged out of the flowcell through a discharging tube 8. When Peltier elements are used for the thermo-modules 2a, 2b, it is possible to perform the heating or the cooling selectively by changing the polarity of the electric current supplied therein. However, it then is necessary to use a power supply having both positive and negative polarities, and thus the system becomes complex in construction and expensive. Moreover, when the heating mode is changed into the cooling mode or vice versa, a dead zone is produced when no current is supplied to the elements 2a, 2b. During this dead zone, if any disturbance occurs, the temperature stability will be affected to a great extent. In addition, in the dead zone, the thermal response and thus the controlling accuracy become worse. Further, if the process of supplying a sample solution into the flowcell and then discharging the solution out of the flowcell is repeated several tens or several hundreds of times in accordance with a given time sequence, the thermal capacity of the flowcell is increased and the difference between the predetermined temperature and the temperature in the flowcell gradually becomes large, so that a temperature off-set is produced.
As mentioned above, it is extremely difficult to quickly set the solution sample successively supplied into the flowcell at the predetermined temperature and to maintain this condition for the desired time period, and thus it is necessary to solve several difficult problems. For example, for each of the respective solution sample, the following very severe requirement might have to be satisfied: the predetermined temperature must be maintained within 37.degree. C..+-.0.2.degree. C. for ten seconds while the sample is disturbed briefly twice, the surrounding temperature is varied from 18.degree. C. to 28.degree. C., and the power supply voltage has a fluctuation of about 10%. In addition, it is necessary to make the whole apparatus small and inexpensive.